HFIP-Promoted Selective Hydroxyalkylation of Aniline Derivatives with Arylglyoxal Hydrates

One-pot sequential synthesis of unsymmetrical diarylmethanes using methylene chloride as a C1-synthon

Bisindolylmethane (BIM) and its derivatives are widely used in the pharmaceutical industry due to their significant biological activities. However, most reported synthetic methods are focused on the synthesis of symmetric BIMs, while the synthesis of unsymmetrical BIMs remains a challenge. Herein, an unprecedented two-step one-pot method to afford unsymmetrically substituted 3,3'-BIM frameworks, using methylene chloride (DCM) as the C1-synthon is reported. In this protocol, the formation of two C-C bonds can be achieved via a one-pot reaction. The utility of commercially available phenols and anilines was also demonstrated in the construction of unsymmetrical diarylmethanes. This protocol provides a straightforward approach to access diverse unsymmetrical diarylmethane derivatives under simple and mild conditions. The broad substrate compatibility and good functional group tolerance of the protocol support its practical application potential.

Gold-Catalyzed "Back-to-Front" Synthesis of 4-Silyloxyindoles

A series of pyrrol-yn-glycol derivatives were easily prepared from simple pyrroles through a three-step sequence involving hydroxyalkylation-alkynylation-O-silylation. Their reaction with IPrAuNTf2 triggers a C2-pyrrole attack onto the activated alkyne and subsequent highly selective 1,2-migration of the oxyalkyl group in the intermediate spirocycle. This approach enables the efficient synthesis of a wide selection of regioselectively functionalized 4-hydroxyindoles, which represent important yet challenging indole scaffolds, in high yields.

HFIP-Promoted Divergent Cycloadditions of Difluoroenoxysilanes with 2-Indolylmethanols: Synthesis of Fluoro 2H-Pyrano[3,4-b]indoles and gem-Difluoro Cyclopenta[b]indoles

An oxa-6π-electrocyclization of difluoroenoxysilanes with diaryl 2-indolylmethanols has been developed. In addition, a rarely reported C3-nucleophilic [3+2] cycloaddition of difluoroenoxysilanes with dialkyl 2-indolylmethanols has been disclosed. This divergent cycloaddition approach affording readily available difluoroenoxysilanes as three-atom and C2 synthons provides rapid access to fluoro 2H-pyrano[3,4-b]indoles and gem-difluoro cyclopenta[b]indoles in good to excellent yields with good functional group tolerance. The metal-free and mild conditions using only HFIP as the solvent without any external acid catalyst illuminate practical and environmentally benign advantages.

Regio- and Stereoselective Hexafluoroisopropoxylation and Trifluoroethoxylation of Allenamides

Incorporating fluorinated moieties into organic molecules is an attractive strategy to enhance drug-like properties. Herein, we have developed a simple and self-promoted protocol for hexafluoroisopropoxylation and trifluoroethoxylation of allenamides with fluorinated alcohols such as HFIP and TFE. The reaction provided the fluoroalkoxylated products in a regio- and stereoselective manner in good to moderate yields under mild conditions.

1,1,1,3,3,3-Hexafluoro-2-Propanol-Promoted Friedel-Crafts Reaction: Metal-Free Synthesis of C3-Difluoromethyl Carbinol-Containing Imidazo[1,2-a]pyridines at Room Temperature

A facile and efficient method has been developed for the synthesis of C3-difluoromethyl carbinol-containing imidazo[1,2-a]pyridines at room temperature via the HFIP-promoted Friedel-Crafts reaction of difluoroacetaldehyde ethyl hemiacetal and imidazo[1,2-a]pyridines. This strategy could be applied to the direct C(sp2)-H hydroxydifluoromethylation of imidazo[1,2-a]pyridines and afford a series of novel difluoromethylated carbinols in good to satisfactory yields with 29 examples. Furthermore, gram-scale and synthetic transformation experiments have also been achieved, demonstrating its potential applicable value in organic synthesis. This green protocol has several advantages, including being transition metal- and oxidant-free, being carried out at room temperature, having high efficiency, and having a wide substrate scope.

C3 Functionalization of Indolizines via HFIP-Promoted Friedel-Crafts Reactions with (Hetero)arylglyoxals

A highly efficient Friedel-Crafts type hydroxyalkylation at the C3 position of indolizines with (hetero)arylglyoxals has been achieved by the action of hexafluoroisopropanol (HFIP) under mild reaction conditions, leading to direct access to a variety of polyfunctionalized indolizines in excellent yields. Installation of more diverse functional groups at the C3 site of indolizine scaffold was realized via further elaboration of the resulting α-hydroxyketone moiety, allowing for expansion of indolizine chemical space.

Synthesis of Difluoromethylated Carbinols via a HFIP-Promoted Hydroxydifluoromethylation of Aniline, Indole, and Pyrrole Derivatives with Difluoroacetaldehyde Ethyl Hemiacetal

A hexafluoroisopropanol (HFIP)-promoted hydroxydifluoromethylation of aniline, indole, and pyrrole derivatives with difluoroacetaldehyde ethyl hemiacetal has been developed. This protocol provides a facile and straightforward approach to access diverse difluoromethylated carbinols in good to excellent yields under mild conditions. Furthermore, gram-scale and synthetic derivatization experiments have also been demonstrated.

Ab Initio Metadynamics Simulations of Hexafluoroisopropanol Solvent Effects: Synergistic Role of Solvent H-Bonding Networks and Solvent-Solute C-H/π Interactions

The solvent effects in Friedel-Crafts cycloalkylation of epoxides and Cope rearrangement of aldimines were investigated by using ab initio molecular dynamics simulations. Explicit molecular treatments were applied for both reactants and solvents. The reaction mechanisms were elucidated via free energy calculations based on metadynamics simulations. The results reveal that both reactions proceed in a concerted fashion. Key solvent-substrate interactions are identified from the structures of transition states with explicit solvent molecules. The remarkable promotion effect of hexafluoroisopropanol solvent is ascribed to the synergistic effect of H-bonding networks and C-H/π interactions with substrates.